Casuarina equisetifolia is a species of Casuarina, native to Australasia, southeastern Asia, and islands of the western Pacific Ocean, from Burma and Vietnam east to French Polynesia, New Caledonia, and Vanuatu, and south to Australia (north of Northern Territory, north and east Queensland, and northeastern New South Wales); it is also possibly native to Madagascar.
In Australia, it is found in a narrow coastal strip from Darwin in the Northern Territory to near Cairns in northern Queensland. The subspecies incana extends southwards from central Queensland to near Port Macquarie, New South Wales and is also found in Vanuatu and New Caledonia.
The genus name is based on the Malay kasuari = the cassowary, referring to the resemblance of the tree's foliage to the cassowary's plumage. The species is named from the Latin equinus = of horses, and folium = leaf, referring to the fine drooping twigs which are reminiscent of horse hair. There are two subspecies: equisetifolia and incana
It is an evergreen tree growing to 6–35 m tall. The foliage consists of slender, much-branched green to grey-green twigs 0.5–1 mm diameter, bearing minute scale-leaves in whorls of 6–8. The flowers are produced in small catkin-like inflorescences; the male flowers in simple spikes 0.7–4 cm long, the female flowers on short peduncles. Unlike most other species of Casuarina (which are dioecious) it is monoecious, with male and female flowers produced on the same tree. The fruit is an oval woody structure 10–24 mm long and 9–13 mm diameter, superficially resembling a conifer cone made up of numerous carpels each containing a single seed with a small wing 6–8 mm long. The crown is finely branched and the branchlets are drooping, needle-like, 20-40 cm long and sometimes hairy. The minute teeth-like reduced leaves are whorls of 7-8. Male flowers occur on simple, terminal, elongated spikes 7-40 mm long and arranged in whorls. Female flowers are on lateral, woody branches. It is wind pollinated. The cones, 10-24 mm long and 9-13 mm in diameter, comprise small, dull brown, winged and single seeded individual fruits, 3-4 mm long. There are about 270 000 viable seeds per kilogram and the seeds germinate readily without pre-treatment.